Color separation of stereo images has been utilized for over fifty years in the production of photographs, 3D movies and the printed page. However, in the prior art devices such as is shown in U.S. Pat. No. 3,712,119, the stereo images are separated by mutually extinguishing filters comprising a blue-green lens filters over one eye and a red filter on the other eye. With this combination, a full true color image is not obtained, and this color combination may cause eye fatigue, and color suppression.
In the present invention the mutually extinguishing filters comprising a special green color for one eye, and a special complementary blue and red color (rose or magenta) for the other eye are comfortable colors to wear; since green and "rose colored glasses" are used as sunglass colors. Idealized multichrome A and B filters, each with a neutral color, are shown in FIGS. 2 and 3 of U.S. Pat. No. 2,543,793, and described in column 6, line 45, to column 7, line 70. These are mutually extinguishing filters A and B with several complementary band pass and band stop characteristics from 400 nm to 700 nm. However, the multichrome filters disclosed in U.S. Pat. No. 2,543,793 are not applicable for the present invention. The filters employed in the practice of the present invention are not multichrome in the sense originally conceived in that they are not neutral color in appearance, rather they are green and magenta in color. However, the term "multichrome" may be employed for the filters of the present invention because the filters are mutually extinguishing; that is, one filter has a band stop characteristic, where the other filter has a band pass characteristic in the same wavelength ranges, and used together over two eyes, a sensation of white is perceived.
The multichrome filters of the present invention are complementary A and B filters defined as a green A filter with a single band pass characteristic and a magenta B filter with a single band stop characteristic; or preferably an A filter with a single band pass, and a B filter with a band stop and band pass characteristic at different portions of the spectrum, as will become apparent hereinafter.
The prior art multichrome filters could not be economically produced, since they were made using interference filters of the multilayer or polarizing type. We have now found dyestuffs to color plastic to make multichrome A and B filters as plastic sheets or films, which can be mounted into cardboard viewers at low cost usable with books, magazines, movies, photos and TV to provide a full-color 3D with comfortable viewing.
The filters of the present invention differ from the photopic/scotopic P and S filters disclosed in our U.S. Pat. No. 3,445,153, in that in contradistinction thereto the A and B filters of the present invention are mutually extinguishing filters, and there is a region of mutual transmission, particularly between 600 and 700 nm, as shown in FIG. 4 of the Patent. More blue light is transmitted in the present filter, resulting in a better balance between red, blue and green portions of the spectrum and better color vision.
The invention utilizes conventional means for the photography of the colored object in 3D; for example, 2 cameras displaced by an interocular distance using a conventional color-photographic film in each. The optical axes of these cameras are adjusted to converge at some point in the object space. For printing 3D color-images on paper in accordance with this invention, conventional color printing inks may be used. One of the images is printed in green and/or yellow and the other image is printed in red and/or blue. The stereo images are displaced in the printing. When seen without the multichrome viewer, printed objects varying greatly in depth appear blurred. However, upon placing the viewers over the eyes, the stereo image and colors are separated. The green and/or yellow color and one stereo image go to the right eye and the blue and/or red color and the second stereo image go to the left eye. The 3-dimensional color images are separated and these right and left colored images proceed via the different optical pathways to different portions of the brain which integrates all the information to provide a full-colored 3D picture.
In this system an object in a single pure color, red, green or blue, would be transmitted only to one eye and so would not appear in stereo. However, pure colors are rare, and most objects are off-white, or pastel shades, and so contain all three primary colors. Thus, most objects will have some component of each color and this enables the separation of right and left stereo images.
We have discovered that certain dyes may be used to achieve this result, which are disclosed hereinafter. These dyes are compatible with various plastic film substrates, such as cellulose acetate, polyvinyl acetate, etc., from which colored films may be produced and fabricated in a known manner to produce the multichrome viewers. To achieve a satisfactory color rendition with multichrome filter pairs A and B, we found that the transmission vs. wavelength characteristics of these colors is critical. A peak transmission averages more than 25% for the green-yellow filter at about 515-540 nm and its transmittance less than 1% from 400 to 475 nm, and from 575 to 700 nm. The magenta filter substantially absorbs the green (which includes yellow) color from 475 and 575 nm; that is, the transmittance is less than 1% in this range. To provide normal color vision, the color balance of the red transmission and blue transmission of the B filter is adjusted relative to the green transmission filter. For example, using 35% peak of the green A filter, the magenta B filter should peak at about 55% at about 435 nm and rise from less than 2% at 580 to about 80% at 700 nm.
While there is a related phenomenon known as "binocular or retinal rivalry".sup.1, we have made a discovery of a new phenomenon in 3D color vision which we term "interocular color suppression". In a set of mutually extinguishing color filters there is a critical choice for the transmission vs. wavelength curve to avoid interocular color suppression. In certain cases interocular color suppression may occur, in which the 3-color vision of both eyes is affected, so that a color in one eye (green) suppresses the color (red) in the other eye, and vice versa; the red and green colors may alternately fade and reappear in a disturbing manner; or may shift to a neutral shade or black. If the green peak is wide, a steady full 3-color image will appear. If the A filter green transmission is too great, relative to the B filter blue and red transmission, color suppression of red may occur. To see all the colors including white, the transmittances of the red, blue and green of the A and B filters must be balanced. Color TV tubes have relative 3-color emissions which have a relatively high intensity, and are balanced to produce a white sensation. Hence color TV tubes in combination with the A and B filters herein described are particularly suitable for 3D TV according to this invention. FNT 1. Page 122, "The Science of Color", Committee on Colorimetry, Optical Society of America, Thomas Y. Crowell Co., 1953, Vail-Ballou Press, Inc., Binghamton, NY
In the prior art filters BG and R shown in FIG. 1, the interocular color suppression is apparent in the dullness of the greens and reds, which are partially suppressed and this may be a cause of the eye fatigue experienced. With the "C" blue and "D" orange (red-green) filter set there is little or no interocular color suppression. The colors remain steady and bright.
Entertainment type color TV tubes utilize red, green and blue phosphors which have standard characteristics which vary little from manufacturer to manufacturer. For example, the Sylvania red phosphor No. 1130 has a peak of 610 nm and a half-width of 3.5 nm; Sylvania No. 1230 green phosphor has a peak of 540 nm and a half-width of 76 nm; and Sylvania No. 1310 blue phosphor has a peak of 435 nm and a half width of 56 nm. The red phosphor is Yttrium oxide or Yttrium oxysulfide, both of which are Europium-doped. The green phosphor is zinc sulfide which is silver-activated. The blue phosphor is also zinc sulfide activated with silver sulfide at a different quantum level.
If the scenes are transmitted in 3D TV, using a CRT (cathode ray tube) TV screen, the green phosphor is employed for a first stereo image to the first eye, and the blue and red phosphors are employed for the second stereo 3D image to the second eye.
In accordance with this invention, the A filter substantially transmits the green phosphor emission and substantially absorbs the blue and red phosphor emissions; and the B filter substantially transmits the blue and red phosphor emissions and substantially absorbs the green phosphor emissions. We have found that in a suitable concentration in a compatible transparent plastic film substrate, a green dye composition may be employed as an A filter; and a magenta dye composition may be employed as a B filter. Formulae for preparing A and B filters are given in Example 4; and for "C" and "D" filters in Example 5.